Cytogenetic studies of pediatric tumors have revealed a number of reproducible karyotypic abnormalities, including del(p13) found in aniridia-Wilms' tumor association, t(8;14) in Burkitt's lymphoma, and t(11;22) in Ewing's sarcoma. To date, no consistent cytogenetic abnormality has been reported in association with hepatoblastoma. We report the case of a 7-month-old male infant with the undifferentiated small cell variant of hepatoblastoma. Immunohistochemistry revealed reactivity with antibodies to cytokeratin and vimentin throughout the tumor. Alpha-fetoprotein, neuron-specific enolase, and S100 stains were negative. Chromosomal analysis of metaphase cells from a culture of tumor tissue revealed a translocation of most of the long arm of chromosome 22 to the distal long arm of chromosome 10.